1. Field of the Invention
The present invention relates to a resist underlayer film composition effective as an antireflective film composition used for microprocessing in manufacturing of a semiconductor device and the like, and to a resist patterning process using the resist underlayer film composition suitable for the exposure to an ultra-violet ray, a KrF excimer laser beam (248 nm), an ArF excimer laser beam (193 nm), a F2 laser beam (157 nm), a Kr2 laser beam (146 nm), an Ar2 laser beam (126 nm), a soft X-ray (EUV, 13.5 nm), an electron beam (EB), an X-ray, and so on.
2. Description of the Related Art
In recent years, as LSI progresses toward a higher integration and a further acceleration in speed, miniaturization of a pattern rule is being requested. Under such circumstance, in a lithography using a photo-exposure that is used nowadays as a general technology, a technology to achieve a finer and more precise pattern processing to a light source used is being developed.
Optical exposure has been widely used using g-line (436 nm) or i-line (365 nm) of a mercury-vapor lamp as a light source for lithography when a resist pattern is formed. It has been considered that a method of using an exposure light with a shorter wavelength is effective as a means for achieving a further finer pattern. For this reason, KrF excimer laser with a shorter wavelength of 248 nm has been used as an exposure light source instead of i-line (365 nm), for mass-production process of a 64 M bit DRAM processing method. However, a light source with far shorter wavelength is needed for manufacture of DRAM with a packing density of 1 G or more which needs a still finer processing technique (a processing dimension of 0.13 μm or less), and lithography using ArF excimer laser (193 nm) has been particularly examined.
In a monolayer resist method used for a typical resist patterning process, it is well known that a pattern fall due to a surface tension of a developer occurs during the time of development if a ratio of a pattern height to a pattern line width (aspect ratio) becomes larger. Accordingly, it has been known that, to form a pattern with a high aspect ratio on a non-planar substrate, a multilayer resist method in which patterning is done by laminating films having different dry etching properties has an advantage; and thus, a bilayer resist method—in which a resist layer formed of a silicon-containing photo-sensitive polymer and an underlayer formed of an organic polymer mainly comprised of elements of carbon, hydrogen, and oxygen, that is for example, a novolak polymer are combined (Japanese Patent Laid-Open (kokai) No. H6-118651 and so on)—and a trilayer resist method—in which a resist layer formed of an organic photo-sensitive polymer used in a monolayer resist method, an intermediate layer formed of a silicon-containing polymer or of a silicon-containing CVD film, and an underlayer formed of an organic polymer are combined—have been developed (Japanese Patent No. 4355943 and so on).
In the underlayer film of the foregoing multilayer resist methods, patterning is done by using the silicon-containing composition layer formed directly thereabove as a hard mask by dry etching with an oxygen gas; and thus, an organic polymer mainly comprised of elements of carbon, hydrogen, and oxygen is used, and at the same time the underlayer film is required to have an etching resistance during the time of dry etching of a substrate to be processed, a film-forming property enabling to form a highly flat film on a substrate to be processed, and, depending on a use method, an antireflective function during the time of an exposure. For example, according to Japanese Patent No. 4355943, which discloses a technology relating to an underlayer film composition for a bilayer or a trilayer resist method, by using an underlayer film such as those disclosed in the document, not only an underlayer film pattern of a high precision can be formed but also a high etching resistance to the etching condition of a substrate to be processed can be secured.
Here, FIG. 2 shows fluctuations of reflectivity of a substrate while k value (extinction coefficient) of an intermediate resist layer is changed.
It follows from FIG. 2 that a sufficient antireflection effect to reduce reflectivity of a substrate to 1% or less can be obtained by making an intermediate resist layer to have a low k value of 0.2 or less and a proper thickness.
In FIG. 3 and FIG. 4, change of reflectance is shown when film thicknesses of the intermediate layer and the underlayer are changed in the cases of k-values of the underlayer film being 0.2 and 0.6. From comparison between FIG. 3 and FIG. 4, it can be seen that, in the case that k-value of the resist underlayer film is higher (in the case of 0.6 (FIG. 4)), reflectance can be reduced to 1% or lower by making the film thickness thereof thinner. In the case that k-value of the resist underlayer film is 0.2 (FIG. 3), in order to obtain reflectance of 1% in film thickness of 250 nm, film thickness of the resist intermediate film needs to be thicker. If film thickness of the resist intermediate film is increased, a load to the resist in the uppermost layer during the time of dry etching in processing of the resist intermediate film increases; and thus, this is not desirable. In FIG. 3 and FIG. 4, reflection in the case of a dry exposure with NA of an exposure equipment lens being 0.85 is shown; it can be seen that, independent of k-value in the underlayer film, reflectance of 1% or lower can be obtained by optimizing n-value (refractive index), k-value, and film thickness of the intermediate layer in the trilayer process.
However, because of an immersion lithography, NA of a projection lens is over 1.0, and angle of an incident light not only to a resist but also to an antireflective film under the resist is becoming shallower. An antireflective film suppresses the reflection not only by absorption due to the film itself but also by a negating action due to an intervention effect of a light. An intervention effect of a light is small in a slant light, and thus, reflection thereof is increased.
Among the films in the trilayer process, it is the intermediate layer that plays an antireflective role by using the intervention action of a light. The underlayer film is too thick for the intervention action so that there is no antireflective effect by a negating effect due to the intervention effect. Reflection from surface of the underlayer film needs to be suppressed; to achieve this, the k-value needs to be made less than 0.6 and the n-value near the value of the intermediate layer thereabove. If a transparency is too high due to a too small k-value, reflection from a substrate takes place; and thus, in the case of NA of an immersion exposure being 1.3, the k-value is optimum in the range between about 0.25 and about 0.48. Target n-values of both the intermediate layer and the underlayer are near the n-value of the resist, namely near 1.7.
As narrowing of a processed line width progresses, phenomena such as wiggling and bending of an underlayer film during etching of a substrate to be processed by using the underlayer film as a mask have been reported (Proc. of Symp. Dry. Process, (2005) p 11). It is generally well known that an amorphous carbon film formed by a CVD method (hereinafter CVD-C film) can very effectively prevent wiggling from occurring because amount of hydrogen atoms therein can be made extremely small.
However, in the case of a non-planar underlayment substrate to be processed, the difference in level needs to be made flat by an underlayer film. By making the underlayer film flat, variance in film thickness of an intermediate film and a photoresist formed thereabove can be suppressed so that a focus margin in lithography can be enlarged.
In the CVD-C film using a raw material such as a methane gas, an ethane gas, and an acetylene gas, it is difficult to fill up the difference in level thereof to flat. On the other hand, in the case that the underlayer film is formed by a spin coating method, there is a merit in that concavity and convexity of the substrate can be filled up.
As mentioned above, the CVD-C film is poor in filling-up of the difference in level, and in addition, introduction of a CVD equipment is sometimes difficult due to its price and occupied footprint area. If a wiggling problem could be solved by using an underlayer film composition capable of forming a film by a spin coating method, merits of simplification in process as well as in equipment thereof would be large.
Accordingly, an underlayer film composition—having optimum n-value, k-value, and filling-up properties as an antireflective film, and having excellent antibending properties without wiggling during etching—and a method for forming an underlayer film having such properties have been sought.